Electrical resistor



Jan. 26, 1960 s. STERN 2,922,974

ELECTRICAL RESISTOR Filed Jan. 28. 195 8 IN VEN TOR. SUMNER STERN mowATTORNEKY United States Patent O ELECTRICAL RESISTOR Sumner Stern,Levittown, Pa., assignor, by mesne assignmeuts, to the United States ofAmerica as represented by the Secretary of the Navy Application January28, 1958, Serial No. 711,761

6 Claims. (Cl. 338-116) This invention relates to electrical circuitcontacts and in particular, to improved electrical contactors employedin magnetic relay devices. 7

Magnetic relays are often used to control contactors in circuitscarrying high direct currents. Since direct current flows as the resultof a continuous voltage applied to a circuit, it does not passperiodically through Zero. Therefore, even'in an absolutelynon-inductive circuit, the full line voltage is available to maintainthe are that forms at the opening contactors. In addition to the linevoltage, there is also an induced voltage generated in any inductancethat may form a part of the circuit. This self-induced voltage is insuch a direction as to oppose a change in the amount of current in thecircuit and, therefore, is in the same direction as the line voltage,and the sum of these two voltages strives to maintain the arc. Arcingresults in pitting of contactor surfaces and eventually to contactorfailure.

Because arcing shortens the operable life of such contactors and limitsthe reliability of them, many efforts have been made to reduce thisarcing. Some of the methods employed include electromagnetic blow-out,absorption circuits, and double break contactors. All of these result inincreased complexity of relay apparatus.

It' is a general object of this invention to eliminate arcing of relaycontrolled circuit contactors.

It is another object of this invention to provide improved relaycontactors having a longer operable life and in which contactor pittingis substantially eliminated.

It is a further object of this invention to provide improved relaycontactors in which arcing is eliminated without adding to thecomplexity of the relay device.

These objects are achieved in this invention by providing at least oneresilient contactor. This resilient contactor is so designed that whenthe circuit is opened only a very small area of the contactor touches anassociated contactor. For circuit closure the resilient contactor iscompressed so that a greater portion of its area touches its associatedcontactor. The resilient contactor itself has a coated surface whichvaries in resistance from a very high resistance at the aforementionedsmall area of contact to a very low resistance when there is a largearea contact. Thus, the resistance on the surface of the contactorvaries from an extreme approaching insulation to one of goodconductivity. The contactors always touch one another even when in theopen circuit position and, although the change from closed to opencircuit is a rapid one, it is still a gradual change. Because of thisgradual change from high conductivity to high resistance no arcingbetween the contactors can occur.

In a preferred embodiment of the invention a pair of resilientcontactors are used. These comprise arcuate springs contacting eachother at their centers. One spring is attached to a bracket which isstationary and the other spring is attached to the movable armature of acontrol relay. One or both of the springs are coated with a resistivematerial as described above. In a modification of 'the preferredembodiment the arcuate spring contactors are replaced by cantilever typesprings. These cantilever springs are coated so as to provide highresistance at their ends and high conductivity inwardly from the ends.The ends of the springs are maintained in contact at the open circuitposition. During compression or release of the cantilever springs agradual change in resistance between them will again occur and arcingwill thus be eliminated.

Other objects and many of the attendant advantages of this inventionwill be described in greater detail by reference to the accompanyingdrawings wherein:

Fig. 1 is a side elevation of a magnetic control relay incorporating theimproved contactors of this invention; open circuit position isillustrated in solid outline and closed circuit position in dottedoutline.

Fig. 2 is a fragmentary view of a magnetic control relay identical tothe relay of Fig. 1 but incorporating improved contactors of cantileverdesign.

Fig. 3a schematically illustrates the variable resistance coating on oneor both of the contactors of Fig. 1.

Fig. 3b similarly illustrates the variable resistance coating on one orboth of the contacts of Fig. 2.

Similar reference characters are applied to similar elements throughoutthe drawings.

In Fig. 1 there is shown a control relay having a U- shaped core 11, anenergizing coil 12, and an armature 13. The armature 13 is hinged at thepivot 14 and completes a magnetic path closing the open end of the U.The outer end of the armature has fastened to it an arcuate spring 15.Opposite the arcuate spring 15 is a like spring 16 supported by abracket 17. Each of the arcuatesprings 15 and 16 have contact terminals18 and 19 associated therewith for attaching thereto the leads of thecircuit to be controlled. The arcuate springs 15 and 16 are shown intheir compressed positions by the dotted outlines 15' and 16.

In Fig. 3a the contacting surfaces of the springs are shown coated witha conductive material. This conductive material might comprise copperfilings suspended in a flexible polystyrene resin.

Another method for constructing variable resistance contacts isdescribed in U.S. Patent 2,060,114, of L. Podolski. The coating isapplied to the spring surface in such a manner that conductivity at thecenter 23 of the spring surface is almost non-existent, that is, thearea '23 in the center of the surface is nearly a pure insulator.

Moving from the center 23 outward to either end the volume of copperfilings in the polystyrene resin is increased until at some area 24 thesurface of the spring becomes a good conductor. It can be seen that whentwo of these springs are juxtaposed, as shown in Fig. 1, their contactat open circuit condition will amount to a near perfect insulator andwill therefore open the circuit connected to the terminals 18 and 19.When the springs are compressed by the energization of the relay, anincreasingly greater portion of the better conductive area of one springwill come in contact with a like area of the other. Hence, when thearmature is fully attracted to the core, the contact surfaces of the twosprings are compressed until the highly conductive areas are touchingeach other to complete the circuit between the two terminals 18 and 19.

In a modification, shown in Fig. 2, cantilever springs 30 and 31 mightwell be considered to comprise the left half of the two arcuate springsshown in Fig. 1. As before, the cantilever springs are connected toterminals 32 and 33 which are in the circuit to be controlled. A

of the springs in Fig. 1.

By incorporating the improved spring contactors of' this invention in arelay controlledcireuit, arcingiscompletely eliminated regardless of thespeed at which the relay-operates; Thisprovides for a greatly increasedlife span and highly improved reliability.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise-than as specifically described.

What is claimed is:

1. In a magnetic relay, a fixed contact and a movable contact connectedto an armature movable directly toward said fixed contact in response tothe actuation of said relay, at least-one of said contacts comprising anarcuate leaf spring with a flat side thereof in opposed relation to theremaining contact and touching said remaining contact over apredetermined area of arc, one of said contacts having a resistancevarying from a very high predetermined value at said predetermined areaof substantially zero at portions of said leaf spring contacting saidremaining contact only when actuation of said relay compresses saidspring, providing a substantially infinite resistance contact when thecontacts are at their open-most position and a substantially shortcircuit contact when at their closed position.

2. In a magnetic relay, an elongated fixed contact, a pivotally mountedarmature movable directly toward said fixed contact in response to theactuation of said relay, the said armature pivoting in a plane parallelto the length of said elongated fixed contact, and an elongated movablecontact mounted upon said armature having a finite length in the sameradial direction as said fixed contact and closing directly in opposedrelation thereto upon the pivoting of said armature, at least one ofsaid contacts comprising an arcuate compressible leaf spring convextoward and touching said remaining contact at a predetermined area ofmaximum resistance, one of said contacts having a gradient of resistancelessening to sub- 4 relay armature, actuating means for moving saidarmature directly toward said fixed contact in a plane parallel to thelength of said elongated fixed contact, and an elongated movable contactmounted upon said armature having a finite length in the same directionas said fixed contact and closing directlyin opposed relation theretoupon the actuation of said armature, at least one of said I contactscomprising an arcuate compressible leaf spring secured at both endsthereof and convex-toward and touching the remaining contact at apredetermined area of maximum resistance betwe'ensaid ends of the arc,one of said contacts having a gradient of resistance lessening from saidarea to substantially zero resistance within the closed coterminouslength of said contacts, whereby operation of said armature compressingsaid spring produces a rolling contiguity between said contactsproceeding from a very high resistance to a substantially stantiallyzero resistance within the closed coterminous lengthof said contacts,whereby actuation of said relay complete connection betweensaidcontacts:

5. In a magnetic relay, an elongated fixedcontact; a relay armature,actuating means for moving said-armature directly toward said fixedcontact in a plane parallel to the length of said elongated fiXed'contact, andan elongated movable contact mounted upon said armature having afinite length in the same direction assaid fixed contact and closingdirectly in opposed relation thereto upon the actuation of saidarmature, at least one of said contacts comprising a cantilever leafspring-convex toward and touching the remaining contact at apredetermined area of maximum resistance, one of saidcontacts having agradient of resistance lessening to substantially zero resistance withinthe closed coterminous length of said contacts, wherebyoperation of saidarmature compressing said spring produces a rolling contiguity betweensaid contacts proceeding from a very high resistance to a substantiallycomplete connection between said contacts.

6. In a magnetic relay', a fixed contact and a movable contact, saidmovable contact being fixed to an armature and being movable directlytoward said fixed contact in response to'the actuation of said-relay,each of said contacts comprising an arcuate leaf spring with the flatsides thereofin opposed relation to each other and touching each otherover a predetermined area of are, one of said contacts having aresistance varying substantially proportionately to its length from avery high predetermined value at said predetermined area tosubstantially zero at portions of said leaf springs contacting eachotheronly when actuation of said relay compresses said spring.

References Cited in the file of this patent UNITED STATES PATENTS1,331,815 Kazenmaier Feb. 24, 1920 2,386,332 Miller Oct. 9, 19452,513,415 Larsen et al July 4, 1950 2,541,852 Zimrner Feb. 13, 1951

